Microsporidia are emerging pathogens that are seen in both immunocompromised and immune competent hosts. They are also important pathogens in agriculture and aquaculture. Due to their ability to be transmitted by food and water they are on the class B bioterrorism list. The International Congress on Microsporidosis will be held in July 2004 at the Institute of Parasitology of the Czech Republic Academy of Sciences. This congress will be the first meeting to bring together the diverse research community that works on the Microsporidia including: physicians, molecular biologists, cell biologists, and parasitologists who work on insects, fish or humans. Research groups from Europe, Russia, Asia, Africa, Canada, and the USA have all agreed to participate. We expect this congress will result in beneficial discussions on the problems involving molecular biology approaches to identification of Microsporidia. In addition, the impact of sequence analysis of different microsporidian species on theories of early eukaryotic evolution, the place of the phylum Microsporidia in the macrosystem of Eukaryotes, as well as phylogenetic interactions between Microsporidian genera, and comparative genome studies, will be discussed. A comparison of host parasite interactions in invertebrate and vertebrate hosts should be helpful in elucidating pathogenic mechanisms of these organisms. The utility of different therapeutic and control strategies as well as new therapeutic agents will be presented. As more data on biochemistry and physiology of Microsporidia are accumulated, the rapid dissemination of this information will be important in advancing research on these pathogens. Exchanging information on in vivo and in vitro models being utilized in studies on microsporidians, discussions on their advantages and disadvantages is anticipated to be of practical interest for many participants. Overall, the goal of this congress is to foster the exchange of information between these diverse groups of scientists leading to advances in research on these emergent pathogens.